Revamp Mandelbrot example: Use a Literal operator to create QString

Create QString at compile time using the literal operator""s instead of
using pointers to characters. This way, no conversion or allocation will
occur at runtime.

Task-number: QTBUG-108861
Pick-to: 6.5
Change-Id: I4fb51d74abbbfa08fb9fddfa90d8afcebd82a7e2
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
(cherry picked from commit ae0d545d31b480ca65e93e5af5f4649caabaa683)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

examples/corelib/threads/mandelbrot/main.cpp

@@ -12,16 +12,18 @@
 #include <QDebug>
 #include <QRect>
 
+using namespace Qt::StringLiterals;
+
 //! [0]
 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
 
     QCommandLineParser parser;
-    parser.setApplicationDescription("Qt Mandelbrot Example");
+    parser.setApplicationDescription(u"Qt Mandelbrot Example"_s);
     parser.addHelpOption();
     parser.addVersionOption();
-    QCommandLineOption passesOption("passes", "Number of passes (1-8)", "passes");
+    QCommandLineOption passesOption(u"passes"_s, u"Number of passes (1-8)"_s, u"passes"_s);
     parser.addOption(passesOption);
     parser.process(app);